1. Field of the Invention
The present invention relates to a controlled atmosphere cutting method using oxygen enrichment and a tool used for the method in a cutting operation performed by a machine tool.
Recently in the field of machine cutting, a cutting technique is demanded for high-efficiency machining, the preservation of nature, the improvement of working environments, and other environmental issues. At present, practical high-speed dry machining is available in the machining field of a small-diameter ball end mill and so on. As a result of an active study of MQL (Minimal Quantity Lubricant) and cold air machining as well as dry machining, a great effect is obtained. These kinds of machining including dry machining will become the mainstream of machining styles in the future. Further, lower machining cost is another major object.
2. Description of the Prior Art
Regarding conventional controlled atmosphere machining which is a kind of dry machining, Japanese Patent No. 2904205 discloses publicly known machining such as cold air machining aimed at an atmosphere of low oxygen. The specification of U.S. Pat. No. 6,135,862 discloses publicly known machining using nitrogen blow at room temperature. Both are performed in an atmosphere of low oxygen to prevent oxidation.
In the former machining, steel is machined by cutting in an atmosphere of inert gas and an oxygen concentration is controlled at about 12%, so that wear on a tool is minimized and a cut surface has the lowest temperature. Particularly in this example, an amount of generated processing heat and solid lubrication of an oxidation product are brought into harmony with each other and a cooling effect and a lubricating effect are achieved by using air. However, a covered container is necessary to obtain an atmosphere, a gas bomb is used for supplying inert gas, and thus problems of cost and workability arise in practical machining.
On the other hand, U.S. Pat. No. 6,135,862 discloses a method in which a device for separating nitrogen gas from the air by a hollow-fiber film is used, nitrogen gas obtained by the device is blown on the cutting edge of a tool, and a steel material is machined in an atmosphere of low oxygen. This method is excellent in practical use and cost.
However, both of the methods are aimed at an atmosphere of low oxygen. Although an atmosphere of low oxygen is generally desirable for a steel material in consideration of prevention of wear caused by oxidation on a tool, some materials such as a titanium alloy considerably become adhesive in an atmosphere of low oxygen and reduce the life of the tool. Moreover, regarding materials which contain a proper amount of a nonmetallic inclusion to form belag and other oxides on a tool and a work material, an atmosphere of low oxygen or a non-oxidative atmosphere are not suitable for stably forming an oxide protective film or adhering the film to a tool.
In addition, as a gas supply nozzle used for controlling an atmosphere of a cut portion, U.S. Pat. No. 6,135,862 discloses a nozzle having a gas supply hole penetrating the shaft of the body of a tool (end mill).
The above configuration is effective to a certain degree because gas is supplied to the cutting edge of the tool in the case where a groove and a hole are formed on a surface of a workpiece. However, in the case of plane cutting and particularly machining of a step-like shape having no cutting material on one side, most atmospheric gas is dispersed to the outer periphery other than the cutting portion of the cutting edge and to a side having no cutting material, so that gas is insufficiently supplied to the cutting edge.